HOUSTON (Reuters) - A towboat fueled with 11,500 gallons (274 barrels) of diesel sank in the Mississippi River at New Orleans overnight but there was no immediate evidence of a spill and the river was not closed, a Coast Guard spokesman said Friday.

A safety zone has been put in place at the scene near the river bank at Marrero, Louisiana, across from New Orleans, to alert and control vessel traffic in the vicinity, but the river remained open, said spokesman Steve Lehmann.

"No injuries were reported. The eight empty barges the towboat was pushing have been secured. And we're working with oil spill responders to secure the fuel or, if there's any in the water, to clean it up," Lehmann said.

"A few pockets of sheen were spotted, but that could just be residue from the sinking," he said. "We're trying to prevent a spill from happening. We have spill responders on the scene, and we're going to keep our eyes open."

The Coast Guard received a report at about 1:10 a.m. CDT (0610 GMT) Friday that the Altro Donna with three crew members aboard, and eight empty barge in tow, hit a piling and sank, the Coast Guard said.

"We are looking into the piling the vessel allided with on the Marrero side of the river to see whether it is remnants left over from an old structure and, if it is, we'll take steps to have it removed," Lehmann said.

The Mississippi River is a major commercial waterway for crude oil and petroleum products and handles more than half of U.S. agricultural exports.

(Reporting by Bruce Nichols; Editing by Lisa Shumaker)